1. Field of the Invention
The present invention relates to audio signal processing, and, in particular, to microphone arrays used for modal beampattern control.
2. Description of the Related Art
With the proliferation of inexpensive digital signal processors and high-quality audio codecs, microphone arrays and associated signal processing algorithms are becoming more attractive as a solution to improve audio communication quality. For room audio conferencing, one attractive microphone array would be a circular array, which allows the beam to be steered to any angle in the horizontal plane around the array.
Circular microphone arrays are an attractive solution for audio pickup of desired sources that are located in the horizontal plane of the array. Typically, circular microphone array beamforming solutions either apply “conventional” delay or filter-sum beamforming techniques or use a cylindrical spatial harmonic decomposition approach. See, e.g., D. E. N. Davies, Circular Arrays, in Handbook of Antenna Design, Vol. 2, Chapter 12, London, Peregrinus (1983), the teachings of which are incorporated herein by reference in its entirety. In both cases, however, one is not able to control the beampattern in the vertical plane (out of the plane of the array). In fact, the vertical beampattern response can actually exceed the in-plane response of the circular array due to modal aliasing of vertical modes that are not controllable with a standard circular array.